Thanks for a clear answer. just to make it sure, if my wallet(s) are HD (which I do by default) I should not mind about keypool size and I can use 10 of 20 for that matter?
Yes. The existence for the keypool previously is mainly to ensure that the backups that the user makes will be at least valid for 100 or 1000 transactions by default. With the introduction of HD wallet, they don't matter anymore since the keys generated will be consistent across every of your wallet files, no matter how many transactions. This is correct only if you haven't changed your password after saving the wallet files.